This from a wiki search on depersonalization disorder & brain fog:
Etiologies: The list of possible etiologies is said to be "endless".[3] The hyperactive presentation is associated with substance withdrawal or intoxication whereas the hypoactive presentation is associated with recent surgery, being in the intensive care unit, or having a terminal illness.[26] The chronic presentation is associated with disseminated cancer, end-stage liver disease, exhaustion, malnutrition, and wasting whereas the acute presentation is associated with fever.[24][25] In alternative medicine, the disease concept known variously as candida-related complex, the yeast syndrome, or candidiasis is said to cause "brain fog".[43][44] Conventional medicine labels this as quackery.[45] On the other hand, the disease concept candidiasis in conventional medicine is known to be associated with clouding of consciousness.[46] The autointoxication disease concept in alternative medicine where intestinal faecal toxins from faecal stagnation poison the brain has long been said to cause clouding of consciousness.[47][48] Conventional medicine also labels this as quackery.[49] On the other hand, conventional medicine recognizes that intestinal faecal toxins can poison the brain and cause a reduced level or "clouding" of consciousness if the liver fails to detoxify it[50][51] and that faecal impaction and urinary retention can cause clouding of consciousness.[52] Alternative doctors describe allergic responses to certain chemicals such as caffeine or mercury as a cause of clouding of consciousness or brain fog respectively.[53][54] Some skeptics of alternative medicine say that "allergic responses do not include "'brain fog'".[54] Ironically, conventional medicine recognizes that allergic responses in general can cause clouding of consciousness, which is of course also known as "mental fog".[55] Conventional medicine recognizes that intestinal tapeworms can cause clouding of consciousness as well.[56]
By the way, thanks Mat.